The researchers have developed a system called EnLighting based on consumer-grade LEDs that, with some modifications both produce light and serve as light sensors. By having individual LEDs alternate between sending modulated light signals and serving as receivers of signals, it is possible to create a network of bulbs that can send messages to each other and connect to devices, while having no discernible effect on room lighting.
Stefan Schmid, a Ph.D. student at Disney Research and ETH Zurich and colleagues shared details of the system at the IEEE International Conference on Sensing, Communication and Networking (SECON) 2016 in London (see EnLighting paper).
“Visible light communication networks conserve the radio spectrum, while also making it difficult to eavesdrop for anyone out of line of sight of the network,” said Markus Gross, vice president at Disney Research.
The bulbs were modified with a Wi-Fi system chip from Qualcomm, the Atheros 3991 and run an embedded version of Linux. Pulse Width Modulation (PWM) based on simple ON-OFF Keying (OOK) is used to generate the PHY layer symbols by LED modulation and is performed by an Atmel ATmega328p microcontroller.
The researchers deployed four such bulbs for their proof-of-concept system. They showed that their system architecture and protocols enabled the bulbs to create stable networks that could support the low bandwidth applications typical of most IoT devices. They also showed it was possible to use the system to estimate the position of devices in the room.
In addition the light bulbs communicate with each other, and this property is crucial not only to support a wide range of IP protocols but also for a number of application scenarios. As neighboring light bulbs can synchronize, the number of data collisions is reduced and connections made stable.
Light bulb beacon identities can be assigned dynamically where a light bulb is switched off, replaced or relocated. In addition light bulb positioning is expected to require a lower computational burden than Bluetooth beacon based systems and hybrid RF- and light-based systems.